Field of the Invention
The present invention relates to an image reading apparatus and an image forming system.
Description of Related Art
Heretofore, an image reading apparatus is known which reads a sheet output from an image forming apparatus, and feeds back this information to the image forming apparatus for the purpose of improving the image quality. This image reading apparatus is provided with an image reading unit which reads a sheet in the entire sheet width direction, for example, a line sensor consisting of imaging devices arranged in a line. The image reading unit reads a sheet conveyed in the system to generate image data. A control unit of the image reading apparatus then calculates the information for performing calibration to adjust the gradation characteristics of images, and adjusting the image positions between the front and back sides of a sheet and the magnification factor.
On the other hand, in recent years, an image reading apparatus is known which is provided further with a unit capable of measuring color information with a higher reliability than an image reading unit, e.g., a colorimetric unit which colorimetrically measure the absolute values of color, for adjusting the reading characteristics of the image reading unit. This image reading apparatus performs a process of comparing, of a sheet (specifically, a target image printed on the sheet), the color information read by the image reading unit with the color information colorimetrically measured by a colorimetric unit to associate the color information read by the image reading unit with the color information colorimetrically measured by the colorimetric unit. By this configuration, the reliability of the color information read by the image reading unit is improved, and therefore it is possible to feed back accurate information to the image forming apparatus. For example, Japanese Patent Published Application No. 2007-171967 discloses an image forming apparatus in which a spectrophotometer and a scanner are arranged in a document conveying path.
Incidentally, a colorimetric unit has a higher resolution of detecting color information than an image reading unit, and therefore, unlike an image reading unit, the detection range of a colorimetric unit does not cover the entirety of the sheet width direction, so that an image is measured on a spot within a limited detection range (view angle). For this reason, there is a problem that paper dust or the like can be attracted to the optical system during paper conveyance to have a great influence in detection accuracy.
Taking into consideration the above circumstances, it is an object of the present invention therefore to provide an image reading apparatus and an image forming system which are hardly affected by noise due to paper dust or the like.